How to test 1FZ-FE EGR Vacuum Modulator Valve Assembly P0401 code (1 Viewer)

[Rollinn]

Hey guys, I have a 97 LC and throwing the pesky P0401 code. It’s actually showing a 2 separate codes on reader but both as P0401. Never seen a duplicate code.

Anyhow it’s in a smog state so need to figure our son easy steps on how to test the modulator in pic. Can I blow air thru one end or which tube to see if air should pass the diaphragm. Either blow or suck not sure which is which on the part. Damn that’s sounds F’n awful .


Anyway just want the easiest process of elimination here.

Thanks all

 

[BTLSHP]

The FSM page 222 for a '94 gives a systematic walk through of the elements that drive that code. Your photo shows what I suspect is one of the more reliable elements (ed.) of the system.

In my case there were two issues:
1) The pintle shaft in the EGR valve next to what is in your photo would not move. It is a bear to get off and clean requiring a 38mm wrench. I soaked mine in Berryman's because of the PEA content and after a couple of hours the shaft responded to vacuum as it should.

2) There is a cast in pipe running from the EGR through the IM to a spot on the top/backside of where the Throttle Body attaches. For a while I could address the code by spraying Berryman's thought the PCV hose connection. The real solution is to remove the TB and the EGR and patiently clean out all the accumulated carbon.

Fortunately, all the little valves under my IM were fine.

 

[ajax1]

The vacuum switching valve under the air intake can get clogged and stop working as well. You can test the switch by following the two yellow wires to the main harness connection by the front of the air intake by power steering res, unplug the connector no and clip two alligator plugs into the connector from the switch then touch to 12 volts, listen for it to click, you could also hook piece vaccumm tubing to it and if it is clicking blow through it, this is the switch that open and closes for vacuum to the egr

 

[Rollinn]

@BTLSHP @ajax1 Thanks guys. I'm on it now. Yea that 38mm nut is grim for sure..

 

[BTLSHP]

@BTLSHP @ajax1 Thanks guys. I'm on it now. Yea that 38mm nut is grim for sure..

I soaked it on and off for several days with PB Blaster. The long wrench broke it free, but I would hav loved a "stubby" to wind it off. I think I reverted to channel locks at some point.

Getting the studs out of the EGR was another POS part of the job. My Torx heads gave out so I went with double 12mm nuts. I never freed the temp sensor.